From: Len Brown <lenb@kernel.org>
Organization: Intel Open Source Technology Center
To: Knut Petersen <Knut_Petersen@t-online.de>
Subject: Re: 2.6.22 regression: thermal trip points
Date: Thu, 2 Aug 2007 17:56:30 -0400
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On Thursday 02 August 2007 04:40, Knut Petersen wrote:

> Kernel 2.6.22 decreases performance by about 50% on my system.
> No, I do not like that. The reason is a broken BIOS, granted, but there
> was a perfect workaround in the kernel that has been dropped.
> 
> mainboard: AOpen i915GMm-hfs, AWARD BIOS
> cpu: Pentium-M 750 (0.8 to 1.86 MHz)
> openSuSE 10.2 with kernel 2.6.22.1
> 
> The cpu fan can not be controled by linux kernel.
> The BIOS will switch on the cpu fan a bit above 50 deg. Celsius.
> The active and passive trip points both are set to 50 deg. Celsius.
> Temperature of the idle cpu at 800 Mhz: 34 to 42 deg. C.
> The BIOS never changes the trip points.
> Cpufreq does work perfectly.
> 
> Previously there was the possibility  to add something like
> 
> echo  "100:0:65:70:0" > /proc/acpi/thermal_zone/THRM/trip_points
> echo  2 > /proc/acpi/thermal_zone/THRM/polling_frequency
> echo ondemand > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
> 
> to e.g. /etc/init.d/boot.local. With 2.6.22 that solution does not exist
> any longer. Now the code in thermal.c slows down the cpu under load
> to prevent "overheating". Kernel compile time increases from about 12
> to 18 minutes. No, I don?t like that, nobody would.
 

Thanks for the sighting, Knut!
This regression is dramatic when put in the terms of 50% performance hit!
I guess the good news is that thermal throttling is doing the job
we are asking it to:-)

The statement above regarding the existence of active trip points
and the kernel not being able to control the fan are inconsistent
with each other.

Please open a sighting for this machine here:

http://bugzilla.kernel.org/enter_bug.cgi?product=ACPI
vs. Power-Thermal
and attach the output from acpidump, cat /proc/acpi/thermal_zone/*/*
and assign it to len.brown@intel.com

BTW. does the board boot and run properly with "acpi=off"?

thanks,
-Len
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